Stacker crane

ABSTRACT

First and second masts of a stacker crane are arrayed in an X direction and extend vertically. Connecting plates are mounted at lower portions and on both side surfaces, facing a Y direction, of the first and second masts, each including an upper portion fixed to the first or second masts, and a lower portion whose width in the X direction is greater than that of the upper portion. First and second lower hollow frames include a pair of hollow members disposed on both sides of the first and second masts in the Y direction and extending in the X direction and are fixed to the lower portions of the connecting plates. Travelling wheels are supported by the connecting plates and roll on a lower guide rail.

TECHNICAL FIELD

The present invention relates to a stacker crane.

BACKGROUND ART

A conventional automated warehouse includes, for example, a pair ofracks, a stacker crane, a warehousing station, and a delivery station.The pair of racks is provided spaced apart by a prescribed spacing inthe forward-rearward direction. The stacker crane is provided moveablyin the left-right direction between the front and rear racks. Thewarehousing station is disposed sideward of one of the racks. Thedelivery station is disposed sideward of the other rack. The racks havenumerous article storage shelves at the top, bottom, left, and right.

The stacker crane includes a travelling truck, a lift platform that isfreely elevatable along a mast provided to the travelling truck, and anarticle transfer apparatus (e.g., a slide fork that is slidably providedin the forward-rearward direction) that is provided to the liftplatform. The travelling truck principally includes a lower frame thatis guided by and travels along a travelling rail (e.g., refer to PatentCitation 1). The lower frame has a pair of parallel side frames, theside frames being linked to one another at a center part in thelongitudinal direction.

CITATION LIST Patent Literature

Patent Citation 1: Japanese Unexamined Patent Application PublicationNo. 2003-237909

SUMMARY OF INVENTION Technical Problem

The mast and the lower frame of a conventional stacker crane are boltedto one another by a flange. In addition, reinforcing ribs are welded tothe mast. A lifting drive mechanism (including a lifting drive motor) iswelded to the mast, and a wheel is joined, as a wheel unit, to the lowerframe.

In recent years, there has been a demand to achieve high performance instacker cranes (high speed performance and highacceleration-deceleration performance of the crane). Furthermore,achieving such performance also increases the stress that acts upon amast base part, and therefore there is also a demand for reinforcingribs that are strong. However, simply increasing the strength of thereinforcing ribs constrains the attachment of the lifting drive part andthe wheels owing to the enlarged reinforcing ribs.

An object of the present invention is to reduce the stress that actsupon a base part of a mast of a stacker crane by using a simple, spacesaving structure.

Technical Solution

A plurality of aspects will be explained below as the technicalsolution. These aspects can be arbitrarily combined as needed.

A stacker crane according to a first aspect of the invention is astacker crane that travels along a rail. The stacker crane includes afirst mast, a second mast, connecting plates, a first lower hollowframe, and a second lower hollow frame.

The first mast and the second mast are disposed spaced apart from oneanother in a travel direction and extend vertically.

The connecting plates include a plate-shaped first plate and aplate-shaped second plate mounted to a lower part and both sidesurfaces, which face a crossing direction crossing the travellingdirection, of the first mast, and a plate-shaped third plate and aplate-shaped fourth plate mounted to a lower part and both sidesurfaces, which face the crossing direction, of the second mast. Thefirst plate and the second plate each have an upper part fixed to thefirst mast and a lower part whose width in the travelling direction isgreater than that of the upper part. The third plate and the fourthplate each have an upper part fixed to the second mast and a lower partwhose width in the travelling direction is greater than that of theupper part.

The first lower hollow frame and the second lower hollow frame are apair of hollow members disposed on outer sides of the connecting platesin the crossing direction on both sides of the first mast and the secondmast in the crossing direction and extending in the travellingdirection. The first lower hollow frame has a first end fixed to anouter side surface of the lower part of the first plate in the crossingdirection and a second end fixed to an outer side surface of the lowerpart of the third plate in the crossing direction. The second lowerhollow frame has a first end fixed to an outer side surface of the lowerpart of the second plate in the crossing direction and a second endfixed to an outer side surface of the lower part of the fourth plate inthe crossing direction.

In this stacker crane, the first mast and the second mast are connectedto the first lower hollow frame and the second lower hollow frame by theconnecting plates. The connecting plates function as ribs that supportthe masts. Accordingly, the stress that acts upon the masts is reduced.As a result, the stacker crane can support higher performance.

The stacker crane may further include: a travelling wheel unit supportedby the connecting plate and configured to roll on a top surface of therail; and a drive wheel unit configured to make contact with a sidesurface of the rail.

In this stacker crane, the drive wheel unit makes contact with the sidesurface of the rail, and, in response, the travelling wheel unit, whichserves as a follower wheel, rolls on the rail. Accordingly, the stressthat acts upon the connecting plate is reduced.

The travelling wheel unit may include a first travelling wheel and asecond travelling wheel provided spaced apart from one another in thetravelling direction. Both shaft ends of the first travelling wheel arerotatably supported by the first plate and the second plate. Both shaftends of the second travelling wheel may be rotatably supported by thethird plate and the fourth plate.

The drive wheel unit may include a pair of first drive wheels providedat the first ends of the first lower hollow frame and the second lowerhollow frame, and a pair of second drive wheels provided at the secondends of the first lower hollow frame and the second lower hollow frame.

A notch that opens downward may be formed in a lower part of theconnecting plate. The stacker crane may further include a rollerattached to the notch and configure to prevent the first lower hollowframe and the second lower hollow frame from floating up from the rail.

In the stacker crane, the attachment of the floating prevention rollerto the notch of the connecting plate from below and the detachment ofthe roller from the connecting plate downward are easy. Thereby, theinspection and replacement of the floating prevention rollers becomeeasy.

The stacker crane further includes a lift platform, a belt, and alifting drive motor. The lift platform is movable along the first mastand the second mast. The belt is attached to the lift platform. Thelifting drive motor is a motor configured to drive the belt and ismounted in a state tilted with respect to the connecting plate.

In this stacker crane, the lifting drive motor is mounted to theconnecting plate, and therefore the stress that acts on the mast isreduced. In addition, because the attitude of the lifting drive motor isin a tilted state, space saving is achieved.

The stacker crane may further include a control unit and a supportmember. The support member, to which the control unit is attached, maybe fixed to the connecting plate.

In this stacker crane, the control unit is mounted to the connectingplate via the support member. Accordingly, space saving is achieved.

Advantageous Effects

In the stacker crane according to the present invention, the stress thatacts upon a base part of a mast can be reduced by using a simple, spacesaving structure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an oblique view of a stacker crane.

FIG. 2 is a side view of the stacker crane.

FIG. 3 is a front view of a lower of the stacker crane.

FIG. 4 is a front view of a travelling truck.

FIG. 5 is a plan view of the travelling truck.

FIG. 6 is a partial front view of a lower frame.

FIG. 7 is a partial plan view of the lower frame.

FIG. 8 is a side view of the lower frame.

FIG. 9 is a front view of a connecting frame.

FIG. 10 is a side view of a drive wheel unit.

FIG. 11 is a front view of the drive wheel unit.

FIG. 12 is a plan view of the drive wheel unit.

FIG. 13 is a cross sectional view taken along the line XIII-XIII in FIG.10.

FIG. 14 is a cross sectional view taken along the line XIV-XIV in FIG.4.

FIG. 15 is a cross sectional view taken along the line XV-XV in FIG. 4.

FIG. 16 is a schematic drawing of hanging belts and pulleys.

FIG. 17 is a front view of a tensioning mechanism.

FIG. 18 is a cross sectional view taken along the line XVIII-XVIII inFIG. 17.

FIG. 19 is a partial front view of the tensioning mechanism.

DESCRIPTION OF EMBODIMENTS (1) Overall Configuration of Stacker Crane 1(General Explanation)

A stacker crane 1 is an article transfer apparatus that travels insidean automated warehouse (not shown). Below, the travelling direction ofthe stacker crane 1 are the X direction, and the width direction of thestacker crane 1 are the Y direction (crossing direction that cross thetravelling direction). In addition, the vertical direction are the Zdirection.

A pair of racks (not shown) is disposed on both sides of the stackercrane 1, one on each side, in the width direction (Y direction). Thepair of racks is disposed such that it sandwiches a travel passageway ofthe stacker crane 1. The pair of racks has a plurality of articlestorage shelves (not shown), and articles are loaded on the shelves. Awarehousing station (not shown) for warehousing the articles is disposedat a lowermost tier of one of the racks, and a delivery station (notshown) for delivering the articles is disposed at a lowermost tier ofthe other rack.

As shown in FIG. 1 and FIG. 2, an upper guide rail 5 a and a lower guiderail 5 b, which extend in the X direction along the travel passageway,are provided inside the automated warehouse. The upper guide rail 5 a isa plate-shaped member that extends perpendicularly downward. As shown inFIG. 4, FIG. 10, FIG. 11, and FIG. 12, the lower guide rail 5 b is Ishaped in a crossing section and includes an erect part 5 c and ahorizontal part 5 d. In greater detail, an upper part of the lower guiderail 5 b is T shaped. The stacker crane 1 is guided moveably along theupper guide rail 5 a and the lower guide rail 5 b. The stacker crane 1can convey articles to and from the plurality of shelves, thewarehousing station, and the delivery station.

As shown in FIG. 1, FIG. 2, and FIG. 3, the stacker crane 1 includes atravelling vehicle 11, a first mast 13 a, a second mast 13 b, and a liftplatform 15.

The first mast 13 a and the second mast 13 b are members for raising andlowering the lift platform 15. The first mast 13 a and the second mast13 b are disposed spaced apart in the X direction. More specifically,the first mast 13 a and the second mast 13 b are disposed such that theysandwich the lift platform 15 in the X direction. The first mast 13 aand the second mast 13 b extend in the Z direction.

The travelling vehicle 11 is an apparatus for moving the first mast 13a, the second mast 13 b, and the lift platform 15. The travellingvehicle 11 includes a travelling vehicle main body 19, a firsttravelling wheel unit 21 a, a second travelling wheel unit 21 b, and atravelling drive mechanism 23.

The travelling vehicle main body 19 constitutes the basic portion of thetravelling vehicle 11. As shown in FIG. 5, FIG. 6, FIG. 7, and FIG. 8,the travelling vehicle main body 19 includes a first lower frame 25 aand a second lower frame 25 b. The first lower frame 25 a and the secondlower frame 25 b are arrayed in the Y direction and extend in the Xdirection.

The first lower frame 25 a and the second lower frame 25 b have linesymmetry and have the same structure. The first lower frame 25 aincludes a first lower hollow frame 27 a and two connecting plates 29(discussed later). The second lower frame 25 b includes a second lowerhollow frame 27 b and two more of the connecting plates 29 (discussedlater).

The first travelling wheel unit 21 a and the second travelling wheelunit 21 b are attached to the travelling vehicle main body 19 atpositions spaced apart in the X direction.

The travelling drive mechanism 23 is a mechanism that generates motivepower for driving the travelling vehicle main body 19. As shown in FIG.1, FIG. 4, and FIG. 5, the travelling drive mechanism 23 includes afirst drive wheel unit 31 a and a second drive wheel unit 31 b. Thefirst drive wheel unit 31 a and the second drive wheel unit 31 b areattached to the travelling vehicle main body 19 spaced apart in the Xdirection. More specifically, the first drive wheel unit 31 a and thesecond drive wheel unit 31 b are attached to both ends of the travellingvehicle main body 19 in the X direction. The first drive wheel unit 31 aand the second drive wheel unit 31 b each include a first drive wheel 33and a second drive wheel 35. In this case, the first drive wheel 33 andthe second drive wheel 35 of the first drive wheel unit 31 a may becalled a first driving wheel and a second driving wheel, and the firstdrive wheel 33 and the second drive wheel 35 of the second drive wheelunit 31 b may be called a third driving wheel and a fourth drivingwheel.

The arrangement of each of the above mechanisms makes it possible todispose the drive wheels using spaces in the X direction of thetravelling vehicle main body 19. Furthermore, increasing the number ofthe drive wheels makes it possible to reduce the size of each of thedrive wheels; as a result, maintenance of the drive wheels becomes easy.

As shown in FIG. 3, FIG. 4, and FIG. 5, the first travelling wheel unit21 a and the second travelling wheel unit 21 b are located respectivelyoutward of the first mast 13 a and the second mast 13 b in the Xdirection. Here, “outward in the X direction” means “on the sides spacedapart from one another in the X direction.” Accordingly, specifically,the first travelling wheel unit 21 a is disposed on the side oppositethe second mast 13 b with respect to the first mast 13 a, and the secondtravelling wheel unit 21 b is disposed on the side opposite the firstmast 13 a with respect to the second mast 13 b. Furthermore, the firsttravelling wheel unit 21 a and the second travelling wheel unit 21 b aredisposed slightly spaced apart from the first mast 13 a and the secondmast 13 b, but they may be adjacent.

In addition, the first drive wheel unit 31 a and the second drive wheelunit 31 b are located respectively outward of the first travelling wheelunit 21 a and the second travelling wheel unit 21 b in the X direction.Here, “outward in the X direction” means “on the sides spaced apart fromone another in the X direction.” Accordingly, specifically, the firstdrive wheel unit 31 a is disposed on the side opposite the secondtravelling wheel unit 21 b with respect to the first travelling wheelunit 21 a, and the second drive wheel unit 31 b is disposed on the sideopposite the first travelling wheel unit 21 a with respect to the secondtravelling wheel unit 21 b. Furthermore, the first drive wheel unit 31 aand the second drive wheel unit 31 b are slightly spaced apart from thefirst travelling wheel unit 21 a and the second travelling wheel unit 21b, but they may be adjacent.

In the above case, the load that acts owing to the first mast 13 a andthe second mast 13 b is supported by the travelling vehicle main body19, the first travelling wheel unit 21 a, and the second travellingwheel unit 21 b, and therefore the first drive wheel unit 31 a and thesecond drive wheel unit 31 b tend not to be affected by wheel pressurefluctuations.

As shown in FIG. 1, the upper parts of the first mast 13 a and thesecond mast 13 b are linked together by a linking member 55 that extendsin the X direction. In addition, as shown in FIG. 1, the first mast 13 aand the second mast 13 b are each provided with a roller mechanism 57that is guided by the upper guide rail 5 a.

The stacker crane 1 includes a lifting drive mechanism 37 (one exampleof a lifting apparatus) for raising and lowering, and thereby driving,the lift platform 15. The lifting drive mechanism 37 includes hangingbelts 39, a first lifting drive motor 41 a, and a second lifting drivemotor 41 b. The lift platform 15 is capable of moving in the Z directionalong the first mast 13 a and the second mast 13 b. Specifically, thelift platform 15 is disposed between the first mast 13 a and the secondmast 13 b in the X direction and is capable of rising and lowering alongthe first mast 13 a and the second mast 13 b (discussed later).Furthermore, portions on both sides of the lift platform 15 are liftablysupported by the first mast 13 a and the second mast 13 b, respectively.The hanging belts 39 are attached to the lift platform 15. The firstlifting drive motor 41 a and the second lifting drive motor 41 b aremotors that drive the hanging belts 39 and are mounted to the firstlower frame 25 a and the second lower frame 25 b in a tilted state.Specifically, upper ends of the first lifting drive motor 41 a and thesecond lifting drive motor 41 b are disposed on sides in the X directionwith respect to lower ends of the first lifting drive motor 41 a and thesecond lifting drive motor 41 b.

The stacker crane 1 further includes a first control unit 45 a, a secondcontrol unit 45 b, and four support members 47. The first control unit45 a and the second control unit 45 b are apparatuses for controllingvarious operations of the stacker crane 1. The first control unit 45 ais supported by and fixed to the two support members 47 disposed on oneside in the X direction. The second control unit 45 b is supported byand fixed to the two support members 47 disposed on the opposite side inthe X direction. The support members 47 are fixed to the first lowerframe 25 a and the second lower frame 25 b. The interior of the firstcontrol unit 45 a and the second control unit 45 b have electricalequipment, such as inverters, converters, and breakers, first travellingdrive motors 81, second travelling drive motors 83, the first liftingdrive motor 41 a, and the second lifting drive motor 41 b.

A transfer apparatus 17 is provided on the lift platform 15. Thetransfer apparatus 17 is an apparatus for transferring articles betweenthe stacker crane 1 and the shelves of the racks. The transfer apparatus17 can place articles thereupon. Furthermore, the transfer apparatus 17can transfer articles from the stacker crane 1 to the shelves of theracks and can transfer articles from the shelves of the racks to thelift platform 15 of the stacker crane 1. The transfer apparatus 17employs a push-pull system that includes a telescoping arm. However, aslide fork system or some other system may be used as the transferapparatus.

In the present embodiment, the connecting plates 29 are thinplate-shaped members; furthermore, because other mechanisms are disposedbetween the pair of connecting plates 29 (between the pair of connectingplates 29 in the Y direction), the dimension of the travelling vehiclemain body 19 in the Y direction is reduced, as shown in FIG. 5. Forexample, travelling wheels 49, the first mast 13 a, the second mast 13b, and the lifting drive mechanism 37 are disposed between the pair ofconnecting plates 29.

(2) Structure of Travelling Vehicle Main Body (Detailed Explanation)

The structure of the travelling vehicle main body 19 will be explainedin greater detail.

As shown in FIG. 8 and FIG. 14, the first lower hollow frame 27 a andthe second lower hollow frame 27 b are made of square pipes havingrectangular cross sections, and the longitudinal direction thereofcoincide with the X direction. As is obvious from the drawings, thefirst lower hollow frame 27 a and the second lower hollow frame 27 b arelonger in the Z direction than in the Y direction and have oblong crosssections. The first lower hollow frame 27 a and the second lower hollowframe 27 b are disposed on opposite sides of the lower guide rail 5 b inthe Y direction. More specifically, the first lower hollow frame 27 aand the second lower hollow frame 27 b are disposed sideward of thelower guide rail 5 b (at positions that overlap when viewed in the Ydirection). As a result, upper surface parts of the first lower hollowframe 27 a and the second lower hollow frame 27 b are disposed atpositions that are higher than the horizontal part 5 d of the lowerguide rail 5 b. Furthermore, the first lower hollow frame 27 a and thesecond lower hollow frame 27 b are joined to one another via anothermember or mechanism.

The first lower hollow frame 27 a and the second lower hollow frame 27 bare disposed on both sides of the first mast 13 a and the second mast 13b in the Y direction and are fixed to the first mast 13 a and the secondmast 13 b via the connecting plates 29 (discussed later).

Furthermore, as shown in FIG. 6, notches 27 e are formed in lower partsof the first lower hollow frame 27 a and the second lower hollow frame27 b at both ends in the X direction. Reinforcing plates 43 are fixed toside surfaces of the notches 27 e in the Y direction. Openings 43 a areformed in the reinforcing plates 43 at positions corresponding to thenotches 27 e.

As shown in FIG. 7 and FIG. 8, the connecting plates 29 are four thinplate-shaped members that are mounted to the lower parts and to bothside surfaces facing the Y direction of the first mast 13 a and thesecond mast 13 b. The flat surfaces of the connecting plates 29 face theY direction. As shown in FIG. 5, those mounted to the first mast 13 aare a first plate 29A and a second plate 29B, and those mounted to thesecond mast 13 b are a third plate 29C and a fourth plate 29D. Theconnecting plates 29 are fixed, by welding, to inner side surfaces ofthe first lower hollow frame 27 a and the second lower hollow frame 27 bin the Y direction. In other words, the first lower frame 25 a includesthe first lower hollow frame 27 a and the two connecting plates 29 (thefirst plate 29A and the third plate 29C) that are fixed, by welding, tothe inner sides thereof in the Y direction and at both ends thereof inthe X direction. In addition, the second lower frame 25 b includes thesecond lower hollow frame 27 b and the two connecting plates 29 (thesecond plate 29B and the fourth plate 29D) that are fixed, by welding,to the inner sides thereof in the Y direction and at both ends thereofin the X direction.

To explain in further detail, the first mast 13A is fixed to inner sidesurfaces of the first plate 29A and the second plate 29B in the Ydirection, and the first lower hollow frame 27 a and the second lowerhollow frame 27 b are fixed to outer side surfaces of the first plate29A and the second plate 29B, respectively, in the Y direction. Thesecond mast 13 b is fixed to inner side surfaces of the third plate 29Cand the fourth plate 29D in the Y direction, and the first lower hollowframe 27 a and the second lower hollow frame 27 b are fixed to outerside surfaces of the third plate 29C and the fourth plate 29D,respectively, in the Y direction.

As explained above, the first mast 13 a is fixed to the first lowerhollow frame 27 a and the second lower hollow frame 27 b via theconnecting plates 29 (the first plate 29A and the second plate 29B,respectively). In addition, the second mast 13 b is fixed to the firstlower hollow frame 27 a and the second lower hollow frame 27 b via theconnecting plates 29 (the third plate 29C and the fourth plate 29D,respectively). In this case, because the thickness of the connectingplates 29 in the Y direction is small, the first mast 13 a and thesecond mast 13 b as well as the first lower hollow frame 27 a and thesecond lower hollow frame 27 b are proximate in the Y direction.Thereby, as shown in FIG. 5, FIG. 7, and FIG. 8, the entire structure iscompact in the Y direction.

As shown in FIG. 9, the connecting plate 29 principally includes anupper part 29 a and a lower part 29 b. The upper part 29 a extends longin the Z direction, and the lower part 29 b extends long in the Xdirection. Accordingly, the width of the lower part 29 b (the Xdirectional length) is greater than the width of the upper part 29 a. Inaddition, the connecting plate 29 has a first tilted surface 29 c thatextends diagonally on the outer side in the X direction and a secondtilted surface 29 d that extends diagonally on the inner side in the Xdirection. The second tilted surface 29 d is provided at a position thatis lower than that of the first tilted surface 29 c. In the connectingplate 29, a notch 29 e, which extends in the Z direction and is open onthe lower side, is further formed in a lower surface of an outer sideportion in the X direction.

As described above, the first tilted surface 29 c and the second tiltedsurface 29 d are formed on the connecting plate 29. These structures arefor blocking any shaking (tilting in the X direction) of the first mast13 a and the second mast 13 b. In the present embodiment, the formationof the first tilted surface 29 c at a comparatively high position iseffective in blocking movement that would cause the first mast 13 a orthe second mast 13 b to topple toward the outer side in the X direction.

The first lower hollow frame 27 a and the second lower hollow frame 27 bare fixed to the lower part 29 b of the connecting plate 29. In greaterdetail, a first end of the first lower hollow frame 27 a is fixed to anouter side surface in the Y direction of the lower part 29 b of thefirst plate 29A, and a second end of the first lower hollow frame 27 ais fixed to an outer side surface in the Y direction of the lower part29 b of the third plate 29C. In addition, a first end of the secondlower hollow frame 27 b is fixed to an outer side surface in the Ydirection of the lower part 29 b of the second plate 29B, and a secondend of the second lower hollow frame 27 b is fixed to an outer sidesurface in the Y direction of the lower part 29 b of the fourth plate29D.

Furthermore, lower ends of the first mast 13 a and the second mast 13 bare fixed to the upper parts 29 a of the connecting plates 29. Ingreater detail, the lower end of the first mast 13 a is fixed to aninner side surface in the Y direction of the upper part 29 a of thefirst plate 29A and to an inner side surface in the Y direction of theupper part 29 a of the second plate 29B. In addition, the lower end ofthe second mast 13 b is fixed to an inner side surface in the Ydirection of the upper part 29 a of the third plate 29C and to an innerside surface in the Y direction of the upper part 29 a of the fourthplate 29D.

As described above, the first mast 13 a and the second mast 13 b arefixed to the first lower hollow frame 27 a and the second lower hollowframe 27 b via the connecting plates 29. In addition, based on the aboveconfiguration, the connecting plates 29 function as ribs that supportthe first mast 13 a and the second mast 13 b. Accordingly, the stressesthat act on the first mast 13 a and the second mast 13 b are reduced. Asa result, higher performance of the stacker crane 1 can be supported.

(3) Travelling Wheel Unit

The first travelling wheel unit 21 a and the second travelling wheelunit 21 b will be explained in further detail.

The first travelling wheel unit 21 a and the second travelling wheelunit 21 b are mounted to the lower parts 29 b of the connecting plates29. As shown in FIG. 3, FIG. 5, and FIG. 14, the first travelling wheelunit 21 a and the second travelling wheel unit 21 b each have thetravelling wheel 49. The travelling wheels 49 function as followerwheels and are configured such that they roll on a top surface of thelower guide rail 5 b (a top surface of the horizontal part 5 d).Accordingly, the stresses that act on the connecting plates 29 arereduced.

Specifically, as shown in FIG. 14, the first travelling wheel unit 21 aincludes a first travelling wheel 49 a, a first shaft member 51 a, and afirst bearing 53 a. The first travelling wheel 49 a is fixed to bothends of the first shaft member 51 a via the first bearing 53 a. As shownin FIG. 14, the first shaft member 51 extends in the Y direction andboth ends thereof are fixed to a pair of the connecting plates 29 (thepair of connecting plates 29 fixed to the first lower hollow frame 27 aand the second lower hollow frame 27 b on one side in the X direction,that is, the first plate 29A and the second plate 29B).

The second travelling wheel unit 21 b has the same structure as that ofthe first travelling wheel unit 21 a and, although not illustrated, hasa second travelling wheel 49 b, a second shaft member (not shown), and asecond bearing (not shown). The second travelling wheel is fixed to bothends of the second shaft member via the second bearing. The second shaftmember extends in the Y direction, and both ends thereof are fixed to apair of the connecting plates 29 (the pair of connecting plates 29 fixedto the first lower hollow frame 27 a and the second lower hollow frame27 b on the opposite side in the X direction, that is, the third plate29C and the fourth plate 29D).

As discussed above, both shaft ends of the first travelling wheel 49 aare rotatably supported by the first plate 29A and the second plate 29B.Both shaft ends of the second travelling wheel 49 b are rotatablysupported by the third plate 29C and the fourth plate 29D. Thus, theconnecting plates 29 have a function that supports the travelling wheels49, which reduces the part count.

(4) Floating Prevention Roller Unit

Furthermore, as shown in FIG. 15, floating prevention roller units 61are mounted to the lower parts 29 b (more specifically, the notches 29e) of the connecting plates 29. Accordingly, the attachment of thefloating prevention roller units 61 to the connecting plates 29 and thedetachment of the floating prevention roller units 61 from theconnecting plates 29 are easy. Thereby, the inspection and replacementof the floating prevention roller units 61 become easy.

More specifically, as shown in FIG. 15, the floating prevention rollerunits 61 are disposed on the inner sides of the connecting plates 29 inthe Y direction and are mounted to the notches 29 e. Each floatingprevention roller unit 61 includes a roller 63, a shaft member 65, and abearing 67. Each roller 63 is disposed proximate to and downward of thehorizontal part 5 d of the lower guide rail 5 b. Each roller 63 isrotatably supported by one end of its corresponding shaft member 65 viaits corresponding bearing 67. Each shaft member 65 is mounted to itscorresponding notch 29 e and, furthermore, another end is fixed to itscorresponding connecting plate 29. Furthermore, bolts 69 that fix theshaft members 65 to the connecting plates 29 can be operated through theopenings 43 a of the reinforcing plates 43 and the notches 27 e of thefirst lower hollow frame 27 a and the second lower hollow frame.Accordingly, the mounting and dismounting of the floating preventionroller unit 61 become easy.

Furthermore, the floating prevention roller units 61 should be moved tothe upper side in the Z direction when being mounted to the notches 29 eand should be moved to the lower side in the Z direction when beingdismounted from the notches 29 e.

Furthermore, because the rotatable rollers 63 are used as a floatingprevention mechanism, even if the travelling vehicle main body 19 wereto float up while travelling (particularly during acceleration anddeceleration), the load between the lower guide rail 5 b and thefloating prevention mechanism can be reduced. As a result, the burden onboth the lower guide rail 5 b and the travelling vehicle main body 19 islessened.

(5) Control Unit

The installation positions of the first control unit 45 a and the secondcontrol unit 45 b will be explained in further detail.

The support members 47 are four members, and one support member 47 isfixed to each of the connecting plates 29. Each support member 47includes a fixed part 47 a and a support part 47 b. One of the fixedparts 47 a is fixed to the outer side surface in the Y direction of eachof the connecting plates 29. The fixing positions of the fixed parts 47a are the upper parts 29 a of the connecting plates 29. The support part47 b extends from the outer side of the fixed part 47 a in the Xdirection. In so doing, as shown in FIG. 3, the first control unit 45 ais disposed on the two support parts 47 b that are on one side end inthe X direction and adjacent in the Y direction, and the second controlunit 45 b is disposed on the two support parts 47 b that are on theopposite side end in the X direction and adjacent in the Y direction.

As discussed above, space saving is achieved because the connectingplates 29 are what fix the first control unit 45 a and the secondcontrol unit 45 b via the support members 47. In particular, as shown inFIG. 3 and FIG. 4, the support parts 47 b of the support members 47 aredisposed proximate to the upper ends of the first lifting drive motor 41a and the second lifting drive motor 41 b. Accordingly, the installationpositions of the first control unit 45 a and the second control unit 45b can be lowered. In particular, as discussed later, because the firstlifting drive motor 41 a and the second lifting drive motor 41 b aretilted and their heights are low, the installation positions of thefirst control unit 45 a and the second control unit 45 b can be lowered.

(6) Travelling Drive Mechanism

The travelling drive mechanism 23 will be further explained.

The first drive wheel unit 31 a and the second drive wheel unit 31 b aremounted to the first lower hollow frame 27 a and the second lower hollowframe 27 b. The first drive wheel unit 31 a and the second drive wheelunit 31 b are each supported by both end parts in the X direction of thefirst lower hollow frame 27 a and the second lower hollow frame 27 b andinclude the first drive wheel 33 and the second drive wheel 35. Thus, aset of the first drive wheel 33 and the second drive wheel 35 isdisposed at each end on both sides of the travelling vehicle main body19 in the X direction; that is, the stacker crane 1 has a total of fourof the drive wheels. As shown in FIG. 4, FIG. 11, and FIG. 12, the firstdrive wheels 33 and the second drive wheels 35 are capable of makingcontact with side surfaces of the lower guide rail 5 b (side surfaces ofthe erect part 5 c).

As shown in FIG. 11 and FIG. 12, the first drive wheel unit 31 a and thesecond drive wheel unit 31 b each include a first wheel supportingportion 71 and a second wheel supporting portion 73. Thus, each set ofthe first wheel supporting portion 71 and the second wheel supportingportion 73 is disposed at each end on both sides of the travellingvehicle main body 19 in the X direction; that is, the stacker crane 1has a total of four of the wheel supporting portions. The first wheelsupporting portions 71 are horizontally pivotably fixed to the firstlower hollow frame 27 a and the second lower hollow frame 27 b of thetravelling vehicle main body 19 (the details of which are discussedlater). The first drive wheel 33 is supported by the first wheelsupporting portion 71 and makes contact with one side surface of thelower guide rail 5 b. As shown in FIG. 10, FIG. 12, and FIG. 13, a lockmechanism 75 unpivotably fixes the first wheel supporting portion 71 tothe first lower hollow frame 27 a and the second lower hollow frame 27 bof the travelling vehicle main body 19 (the details of which arediscussed later).

The second wheel supporting portion 73 is horizontally pivotably fixedto the first lower hollow frame 27 a and the second lower hollow frame27 b of the travelling vehicle main body 19 (the details of which arediscussed later). The second drive wheel 35 is supported by the secondwheel supporting portion 73 and makes contact with another side surfaceof the lower guide rail 5 b. A pressing mechanism 77 (one example of apressing mechanism) urges the first wheel supporting portion 71 and thesecond wheel supporting portion 73 in a direction that narrows thespacing between them, and that urging can be released by the removal ofthe pressing mechanism 77. In addition, the abovementioned mechanismmakes a guide roller unnecessary.

In the stacker crane, the first drive wheels 33 and the second drivewheels 35 clamp the side surfaces of the lower guide rail 5 b by theurging of the pressing mechanisms 77. The travelling vehicle main body19 travels in this state, and therefore variation in wheel pressuretends not to occur.

In addition, the impact of wheel pressure fluctuation is small, andtherefore the pressing force that acts on the drive wheels can be set toa proper value that is not excessively large. As a result, the size ofthe drive wheels can be reduced or the lifespan of the drive wheels canbe extended. Conventionally, if the left-right balance degrades owing towheel pressure fluctuations, the size of the drive wheels must beincreased in order to handle a larger load.

In addition, the first wheel supporting portions 71 are unpivotablyfixed to the travelling vehicle main body 19 by way of the lockmechanisms 75. However, if the pressing mechanisms 77 are detached and,furthermore, the lock mechanisms 75 are released, then the first wheelsupporting portions 71 and the second wheel supporting portions 73 canboth pivot in direction away from one another. Thereby, the first drivewheels 33 and the second drive wheels 35 become spaced apart from thelower guide rail 5 b, and the maintenance (replacement, adjustment, andrepair) of both drive wheels becomes easy.

The travelling drive mechanism 23 includes the first travelling drivemotors 81 and the second travelling drive motors 83. By virtue of beingfixed to the first wheel supporting portions 71, the first travellingdrive motors 81 are horizontally pivotable with respect to both thefirst drive wheels 33 and the travelling vehicle main body 19. The firsttravelling drive motors 81 are capable of driving the first drive wheels33. By virtue of being fixed to the second wheel supporting portions 73,the second travelling drive motors 83 are horizontally pivotable withrespect to both the second drive wheels 35 and the travelling vehiclemain body 19. The second travelling drive motors 83 are capable ofdriving the second drive wheels 35. Thus, a set of the first travellingdrive motor 81 and the second travelling drive motor 83 is disposed ateach end on both sides of the travelling vehicle main body 19 in the Xdirection; that is, the stacker crane 1 has a total of four travellingdrive motors. In this case, because the first travelling drive motors 81and the second travelling drive motors 83 can horizontally pivot withrespect to the first wheel supporting portions 71 and the second wheelsupporting portions 73, respectively, the torque transmitting mechanismof the motor during maintenance is spaced apart from the lower guiderail and consequently does not interfere with maintenance.

The second drive wheel 35 of the first drive wheel unit 31 a and thesecond drive wheel 35 of the second drive wheel unit 31 b are disposedon the same side of the lower guide rail 5 b in the Y direction.Accordingly, the stacker crane 1 can travel stably and rectilinearly.

The structure wherein the first wheel supporting portions 71 and thesecond wheel supporting portions 73 pivot freely will be explained indetail.

As shown in FIG. 10 through FIG. 12, the first wheel supporting portion71 and the second wheel supporting portion 73 each include a supportmember 87 and a pivoting support member 89. The support member 87 is amember including a plurality of plates extending in the X direction and,owing to the pivoting support member 89, the inner side end in the Xdirection of the support member 87 pivots freely in the horizontaldirection with respect to the first lower hollow frame 27 a and thesecond lower hollow frame 27 b. Namely, the pivoting centers of thefirst wheel supporting portion 71 and the second wheel supportingportion 73 are the pivoting support members 89. As shown in FIG. 11 andFIG. 12, the first drive wheel 33 and the first travelling drive motor81 as well as the second drive wheel 35 and the second travelling drivemotor 83 are fixed to the support members 87. Each pivoting supportmember 89 includes a pin 91 that extends in the Z direction. The pins 91are attached to protruding plates 27 c, which are provided on outer sideend parts in the X direction of the first lower hollow frame 27 a andthe second lower hollow frame 27 b, and furthermore pivotably supportthe support members 87 in the horizontal direction.

As discussed above, the position of the first drive wheel 33 and thesecond drive wheel 35 and the position of the pivoting support members89 differ (they are spaced apart in the X direction as shown in FIG. 12)and therefore, when the first wheel supporting portion 71 or the secondwheel supporting portion 73 pivots, the first drive wheel 33 or thesecond drive wheel 35 moves such that it describes an arcuate trajectoryin a plan view. Furthermore, as shown in FIG. 12, the position at whichthe first drive wheel 33 contacts the lower guide rail 5 b and theposition at which the second drive wheel 35 contacts the lower guiderail 5 b coincide in the X direction.

The structure and the function of the lock mechanism 75 will beexplained in detail.

The lock mechanism 75 is a mechanism for limiting the pivoting of thefirst wheel supporting portion 71, the first drive wheel 33, and thefirst travelling drive motor 81 in the horizontal direction. As shown inFIG. 13, the lock mechanism 75 includes plates 93, collars 94, bolts 95,and nuts 96. The plates 93 are a pair of members extending from thelower part of the first travelling drive motor 81. The plates 93 aredisposed on the upward apparatus side and the downward apparatus side ofa pair of protruding parts 27 d provided at outer side end parts in theX direction of the first lower hollow frame 27 a and the second lowerhollow frame 27 b. The collars 94 are disposed such that they passthrough holes formed in the plates 93 and the protruding parts 27 d.Main body portions of the bolts 95 pass through the interior of thecollars 94, and the nuts 96 are screwed onto tips of the bolts 95. Inthis way, owing to the bolts 95 and the nuts 96, the collars 94 cannotcome off of the plates 93 and the protruding parts 27 d. As a result,the plates 93, namely, the first wheel supporting portion 71, the firstdrive wheel 33, and the first travelling drive motor 81, cannot pivot inthe horizontal direction owing to the collars 94.

Furthermore, if the bolts 95 and the nuts 96 are operated and thecollars 94 are removed, then the plates 93, namely, the first wheelsupporting portion 71, the first drive wheel 33, and the firsttravelling drive motor 81, become pivotable in the horizontal direction.

The structure and the function of the pressing mechanism 77 will beexplained in detail.

The pressing mechanism 77 includes a shaft 101 and an elastic member107. As shown in FIG. 10, FIG. 11, and FIG. 12, the shaft 101 isdisposed on outer sides of the pair of support members 87 in the Xdirection and extends in the Y direction. Both ends of the shaft 101pass through protruding parts 87 a, which are provided on outer sides ofthe support members 87 in the X direction. A first end 101 a of theshaft 101 is fixed by a nut and a plate 103 to the protruding part 87 aof the support member 87 of the second wheel supporting portion 73. Asecond end 101 b of the shaft 101 is elastically supported in the Ydirection by the elastic member 107. Specifically, the elastic member107 is disposed at the protruding part 87 a of the support member 87 ofthe first wheel supporting portion 71 on the side opposite the secondwheel supporting portion 73 and is supported by a nut and a plate 105that are fixed to the second end 101 b of the shaft 101. The elasticmember 107 is compressed in the Y direction between the protruding part87 a on one side and the nut and the plate 105 on the other side;accordingly, the elastic member 107 imparts an urging force to the firstwheel supporting portion 71 and the second wheel supporting portion 73such that they draw near in the Y direction. As a result, the firstdrive wheel 33 and the second drive wheel 35 make contact with, suchthat they clamp the side surfaces of the lower guide rail 5 b (bothsurfaces of the erect part 5 c). Furthermore, the elastic member 107 isa spring, for example, a compression coil spring.

Furthermore, the first wheel supporting portion 71 and the second wheelsupporting portion 73 can be removed by, in the pressing mechanism 77,removing the nut and the plate 103 as well as the nut and the plate 105from the shaft 101 and, furthermore, pulling the shaft 101 out of theprotruding part 87 a.

Furthermore, the type of the pressing mechanism is not limited to theabovementioned embodiment. In particular, the structure that attachablyand detachably links to the wheel supporting portions is not limited tothe combination of the shaft, the nuts, and the plates. In addition, thepresence or absence, the type, and the arrangement position of theelastic member is not limited to the abovementioned embodiment.

(7) Lifting Drive Mechanism

As schematically shown in FIG. 16, the lifting drive mechanism 37includes the lift platform 15, the pair of hanging belts 39, a pair ofupper pulleys 117, a pair of drive pulleys 119, a pair of idler pulleys121, lower pulleys 123, the first lifting drive motor 41 a, and thesecond lifting drive motor 41 b.

The drive pulleys 119, the idler pulleys 121, and the lower pulleys 123are rotationally supported by the pair of connecting plates 29. Thedirection in which the rotary shafts of these pulleys extend are the Ydirection. More specifically, both shaft ends of the drive pulleys 119and the idler pulleys 121 are directly supported by the pair ofconnecting plates 29, and both shaft ends of the lower pulleys 123 aresupported by the pair of connecting plates 29 via supporting members 127(discussed later) of tensioning mechanisms 125 (discussed later). Thatis, the drive pulleys 119, the idler pulleys 121, and the lower pulleys123 are disposed between the pair of connecting plates 29 in the Ydirection.

As is clear from the drawings, each member of the lifting drivemechanism 37 is provided symmetrically at both ends in the X direction,and therefore the configuration of only one side in the X direction willbe explained below.

The hanging belt 39 is an endless drive belt that includes a first end39 a, which is fixed to an upper part of the lift platform 15, and asecond end 39 b, which is fixed to a lower part of the lift platform 15.The upper pulley 117 is disposed at the upper end—one upper pulley 117per upper end—of the first mast 13 a and the second mast 13 b. The drivepulley 119 has a function that moves the hanging belt 39 forward and inreverse by the driving force of the first lifting drive motor 41 a orthe second lifting drive motor 41 b. The idler pulley 121 is disposed inthe vicinity of the drive pulley 119 and, more specifically, is disposedupward of and on the inner side in the X direction of the drive pulley119. The lower pulley 123 is disposed at the lower part—one lower pulley123 per lower part—of the first mast 13 a and the second mast 13 b. Thelower pulley 123 is disposed on the inner side of the drive pulley 119in the X direction. The hanging belt 39 is looped around, in orderstarting from the first end 39 a, the upper pulley 117, the idler pulley121, the drive pulley 119, and the lower pulley 123, and ends at thesecond end 39 b.

As shown in FIG. 5, the first lifting motor 41 a and the second liftingdrive motor 41 b are fixed to outer side portions of the lower parts 29b of the connecting plates 29 in the X direction. Because the firstlifting drive motor 41 a and the second lifting drive motor 41 b arefixed to the connecting plates 29 rather than to the first mast 13 a andthe second mast 13 b, the stress that acts on the first mast 13 a andthe second mast 13 b is reduced. In addition, because the attitude ofthe first lifting drive motor 41 a and the second lifting drive motor 41b is in a tilted state, space saving in the Z direction is achieved morethan it would be in an erect state. Furthermore, that the first liftingdrive motor 41 a and the second lifting drive motor 41 b are tiltedmeans the state wherein their main bodies are disposed such that theirupper parts are positioned offset to the outer side in the X directionwith respect to their lower parts. Accordingly, the size of the firstlifting drive motor 41 a and the second lifting drive motor 41 b in theY direction is not increased.

More specifically, the first lifting drive motor 41 a is fixed to anouter side surface of the second plate 29B in the Y direction, and thesecond lifting drive motor 41 b is fixed to an outer side surface of thefourth plate 29D in the Y direction. That is, the first lifting drivemotor 41 a and the second lifting drive motor 41 b are disposed on theouter sides of the pair of connecting plates 29 in the Y direction; thatis, the first lifting drive motor 41 a and the second lifting drivemotor 41 b are disposed at positions offset to one side (the upper sidein FIG. 5) in the Y direction from the center of the travelling vehiclemain body 19 in the Y direction, and therefore the space between thepair of connecting plates 29 can be effectively utilized. In particular,because the first lifting drive motor 41 a and the second lifting drivemotor 41 b are disposed on the same side in the Y direction, access toboth is simplified.

The lifting drive mechanism 37 includes the tensioning mechanisms 125.The tensioning mechanisms 125 are mechanisms that apply tension to thehanging belts 39 by urging the lower pulleys 123 downward. Thetensioning mechanisms 125 are disposed between pairs of the connectingplates 29 (between the first plate 29A and the second plate 29B, andbetween the third plate 29C and the fourth plate 29D).

As shown in FIG. 17, FIG. 18, and FIG. 19, the tensioning mechanism 125includes the supporting members 127 and a supporting-member-fixingmechanism 129. The supporting members 127 are disposed between (in the Ydirection) the first plate 29A and the second plate 29B. The supportingmembers 127 are a pair of plate members that rotationally support bothends of the rotary shaft of the lower pulley 123. The supporting members127 extend long in the X direction, and the lower pulley 123 isrotationally supported by a first end part 127 a.

The supporting members 127 have an intermediate part that is pivotablysupported around a fulcrum S with respect to the connecting plates 29.Specifically, the fulcrum S is implemented by virtue of both ends of apin 139—the pin 139 extending in the Y direction and being fixed to thesupporting members 127 in the vicinity of the middle of the supportingmembers 127 in the X direction—being rotationally supported by theconnecting plates 29. Thus, the supporting members 127 are pivotablearound the fulcrum S, which is spaced apart from the center of rotationof the lower pulley 123 in the X direction. Specifically, the supportingmembers 127 have the first end parts 127 a and second end parts 127 b,which are portions disposed on both sides of the fulcrum S. The firstend parts 127 a rotationally support the lower pulley 123, and thesecond end parts 127 b are positioned by the supporting-member-fixingmechanism 129.

Furthermore, the first end parts 127 a of the supporting members 127 areportions that extend on one side of the fulcrum S in the X direction,and one point of each of the first end parts 127 a is a support partthat supports the lower pulley 123. In addition, the second end parts127 b are portions that extend on the opposite side of the fulcrum S inthe X direction, and one point of each of the second end parts 127 b isa supported part that is supported and fixed by thesupporting-member-fixing mechanism 129.

The supporting-member-fixing mechanism 129 is a mechanism thatdetermines the tension applied to the hanging belt 39 by fixing theattitude of the supporting members 127. Specifically, thesupporting-member-fixing mechanism 129 pivots the supporting members 127by changing the position of the second end parts 127 b of the supportingmembers 127 in the up and down direction, and thereby changes theposition of the first end parts 127 a of the supporting members 127,namely, the position of the lower pulley 123. Furthermore, thesupporting-member-fixing mechanism 129 fixes the attitude of thesupporting members 127 by fixing the position of the second end parts127 b of the supporting members 127 in the up and down direction.

The objects to which the supporting-member-fixing mechanisms 129 areattached are the first plate 29A and the third plate 29C. That is, theconnecting plates to which the lifting drive motors are mounted and theconnecting plates to which the supporting-member-fixing mechanisms areprovided are different. In particular, the supporting-member-fixingmechanisms 129 are disposed on the same side in the Y direction, andtherefore access to both is simplified.

Each supporting-member-fixing mechanism 129 includes a screw member 131,a pin 133, a linking member 135, and two nuts 137. The screw member 131extends in the Z direction and is fixed to, for example, the first plate29A in the vicinity of the second end parts 127 b of the supportingmembers 127. The pin 133 extends in the Y direction from the second endparts 127 b of the supporting members 127, specifically, toward thescrew member 131. The linking member 135 has a portion that rotationallysupports the pin 133 and a plate-shaped portion wherein a hole throughwhich the screw member 131 passes is formed. The two nuts 137 arescrewed onto the screw member 131 and disposed on both sides of theplate-shaped portion of the linking member 135 in the Z direction.

Based on the above structure, if, for example, the two nuts 137 aremoved to the upper side in the Z direction, then, as shown in FIG. 19,the second end parts 127 b of the supporting members 127 move upward viathe linking member 135 and the pin 133 and, attendant therewith, thesupport members 27 pivot around the fulcrum S owing to the pin 139; as aresult, the first end parts 127 a of the supporting members 127 move tothe lower side in the Z direction. Attendant therewith, the lower pulley123 also moves to the lower side in the Z direction, and the Zdirectional position of the lower pulley 123 changes to the lower sideof the Z directional position of the drive pulley 119.

Furthermore, the operation of the two nuts 137 can be performed from anopening 29 f (refer to FIG. 6 and FIG. 9) formed in the first plate 29A,which serves as a sidewall. Thus, by virtue of being disposed between(in the Y direction) the pairs of connecting plates 29 (e.g., the firstplate 29A and the second plate 29B), the hole of each of the tensioningmechanisms 125 can be made compact, and the operation of adjusting themcan be performed from the outer sides (the outer sides in the Ydirection) of the pairs of connecting plates 29, which makes for goodease of operation.

Thus, in each tensioning mechanism 125, the supporting members 127 arepivoted to change the position of the lower pulley 123 for the purposeof applying tension to the hanging belt 39. Furthermore, the fulcrum Sof the pivoting of the supporting members 127 that support the lowerpulley 123 is at a position spaced apart from a center of rotation R ofthe lower pulley 123 in the horizontal direction. Based on the abovestructure, the tensioning mechanism 125 is a compact structure in the Zdirection. For example, only space for a margin of adjustment should beensured in the first mast 13 a and the second mast 13 b. That is, deadspace inside the first mast 13 a and the second mast 13 b does notbecome large. In addition, because a tension adjusting mechanism is notdisposed in the up and down direction of the lower pulley 123, the mostlowered position of the lift platform 15 can be made sufficiently low.

As shown in FIG. 4, FIG. 7, FIG. 17, and FIG. 19, the fulcrum S of thesupporting members 127 is disposed at a position that overlaps the firstmast 13 a or the second mast 13 b in a plan view. In addition, at leastpart of the lower pulley 123 is disposed at a position that is shifted,to the lift platform 15 side, from the position that overlaps the firstmast 13 a or the second mast 13 b in a plan view. More specifically, inthe state shown in FIG. 17, the whole lower pulley 123 is completelyshifted from the first mast 13 a or the second mast 13 b; in the stateshown in FIG. 19, part of the lower pulley 123 overlaps the first mast13 a or the second mast 13 b but mostly is shifted. In other words, evenif the lower pulley 123 is disposed most to the mast side, the lowerpulley 123 does not move to a position at which it substantially orcompletely intrudes upon the mast in a plan view. Based on the abovepositional relationships, by setting the lower pulley 123 at a positionshifted to the lift platform 15 side from the first mast 13 a or thesecond mast 13 b while disposing the fulcrum S of the supporting members127 at the same position as the first mast 13 a or the second mast 13 b,the dead space inside the first mast 13 a and the second mast 13 b canbe made small.

In addition, because the structure that swivels the supporting members127 is adopted, the load for applying tension can be increased, even ifthe generated load is small, if the principle of the lever is used.

Furthermore, the number and positions of the idler pulleys are notlimited to the abovementioned embodiment. For example, the idler pulleymay be provided on the side opposite the idler pulley in theabovementioned embodiment with respect to the drive pulley, or may beprovided on both sides of the drive pulley.

(8) Operational Effects of Connecting Plate

Space saving is achieved by the attachment of various mechanisms to theconnecting plates 29. In particular, because the connecting plates 29are thin plate-shaped members whose principal surfaces face the Ydirection (that is, they have no thickness in the Y direction), they areeffective for space saving. In addition, because the connecting plates29 are thin plate-shaped members, desirable shapes can be implemented asneeded.

In addition, the portions through which the first mast 13 a and thesecond mast 13 b are inserted lie between the pairs of connecting plates29; however, because the inner side surfaces of the connecting plates 29in the Y direction are machined with high precision, the attitudes ofthe first mast 13 a and the second mast 13 b are more accurate.

In particular, because various mechanisms are provided on the connectingplates 29, there is no need to provide these mechanisms on the firstmast 13 a and the second mast 13 b. As a result, the assembly processbelow becomes possible.

-   -   Prepare the first lower frame 25 a and the second lower frame 25        b.    -   Produce the unit by assembling the various mechanisms onto the        connecting plates 29 of the first lower frame 25 a and the        second lower frame 25 b.    -   Transport the abovementioned unit and the masts to the site and        assemble both on site. That is, because only the work of        assembling the masts is performed onsite, working efficiency        improves.

(9) Other Embodiments

The above explained one embodiment of the present invention, but thepresent invention is not limited to the abovementioned embodiment, andit is understood that various modifications may be effected withoutdeparting from the spirit of the invention. In particular, theembodiments and modified examples written in the present specificationcan be combined arbitrarily as needed.

INDUSTRIAL APPLICABILITY

The present invention can be widely adapted to stacker cranes having amast and a lower truck.

REFERENCE SIGNS LIST

-   1 Stacker crane-   5 a Upper guide rail-   5 b Lower guide rail-   5 c Erect part-   5 d Horizontal part-   11 Travelling vehicle-   13 a First mast-   13 b Second mast-   15 Lift platform-   17 Transfer apparatus-   19 Travelling vehicle main body-   21 a First travelling wheel unit-   21 b Second travelling wheel unit-   23 Travelling drive mechanism-   25 a First lower frame-   25 b Second lower frame-   27 a First lower hollow frame-   27 b Second lower hollow frame-   27 c Protruding plate-   27 d Protruding part-   27 e Notch-   29 Connecting plate-   29A First plate-   29B Second plate-   29C Third plate-   29D Fourth plate-   29 a Upper part-   29 b Lower part-   29 c First tilted surface-   29 d Second tilted surface-   29 e Notch-   29 f Opening-   31 a First drive wheel unit-   31 b Second drive wheel unit-   33 First drive wheel-   35 Second drive wheel-   37 Lifting drive mechanism-   39 Hanging belt-   39 a First end-   39 b Second end-   41 a First lifting drive motor-   41 b Second lifting drive motor-   43 Reinforcing plate-   43 a Opening-   45 a First control unit-   45 b Second control unit-   47 Support member-   47 a Fixed part-   47 b Support part-   49 a First travelling wheel-   49 b Second travelling wheel-   51 a First shaft member-   53 a First bearing-   55 Linking member-   57 Roller mechanism-   61 Floating prevention roller unit-   63 Roller-   65 Shaft member-   67 Bearing-   69 Bolt-   71 First wheel support part-   73 Second wheel support part-   75 Lock mechanism-   77 Pressing mechanism-   81 First travelling drive motor-   83 Second travelling drive motor-   87 Support member-   87 a Protruding part-   89 Pivoting support member-   91 Pin-   93 Plate-   93 a Hole-   94 Collar-   95 Bolt-   101 Shaft-   101 a First end-   101 b Second end-   103 Nut and plate-   105 Nut and plate-   107 Elastic member-   117 Upper part pulley-   119 Drive pulley-   121 Idler pulley-   123 Lower pulley-   125 Tensioning mechanism-   127 Support member-   127 a First end part-   127 b Second end part-   129 Supporting-member-fixing mechanism-   131 Screw member-   133 Pin-   135 Linking member-   137 Nut-   139 Pin

1-13. (canceled)
 14. A stacker crane that travels along a rail,comprising: a first mast and a second mast spaced apart from one anotherin a travelling direction and extending vertically; connecting platesincluding a plate-shaped first plate and a plate-shaped second platemounted to a lower portion and both side surfaces, which face a crossingdirection crossing the travelling direction, of the first mast, and aplate-shaped third plate and a plate-shaped fourth plate mounted to alower portion and both side surfaces, which face the crossing direction,of the second mast, the first plate and the second plate each includingan upper portion fixed to the first mast and a lower portion whose widthin the travelling direction is greater than that of the upper portion,and the third plate and the fourth plate each including an upper portionfixed to the second mast and a lower portion whose width in thetravelling direction is greater than that of the upper portion; and afirst lower hollow frame and a second lower hollow frame including apair of hollow members disposed on outer sides of the connecting platesin the crossing direction on both sides of the first mast and the secondmast in the crossing direction and extending in the travellingdirection, the first lower hollow frame including a first end fixed toan outer side surface of the lower portion of the first plate in thecrossing direction and a second end fixed to an outer side surface ofthe lower portion of the third plate in the crossing direction, and thesecond lower hollow frame including a first end fixed to an outer sidesurface of the lower portion of the second plate in the crossingdirection and a second end fixed to an outer side surface of the lowerportion of the fourth plate in the crossing direction; a firsttravelling wheel unit including a first travelling wheel including bothshaft ends rotatably supported by the first plate and the second plate,the first travelling wheel being configured to roll on an upper surfaceof the rail; a second travelling wheel unit including a secondtravelling wheel including both shaft ends rotatably supported by thethird plate and the fourth plate, the second travelling wheel beingconfigured to roll on the upper surface of the rail; and a drive wheelunit configured to contact a side surface of the rail.
 15. The stackercrane according to claim 14, wherein the first travelling wheel unit isdisposed on a side opposite to the second mast with respect to the firstmast; and the second travelling wheel unit is disposed on a sideopposite to the first mast with respect to the second mast.
 16. Thestacker crane according to claim 14, wherein the drive wheel unitincludes a pair of first drive wheels provided at the first ends of thefirst lower hollow frame and the second lower hollow frame, and a pairof second drive wheels provided at the second ends of the first lowerhollow frame and the second lower hollow frame.
 17. The stacker craneaccording to claim 14, wherein a notch that opens downward is located ina lower portion of one of the connecting plates; and the stacker cranefurther comprises a roller attached to the notch and configured toprevent the first lower hollow frame and the second lower hollow framefrom floating up from the rail.
 18. The stacker crane according to claim15, wherein a notch that opens downward is provided in a lower portionof one of the connecting plates; and the stacker crane further comprisesa roller attached to the notch and configured to prevent the first lowerhollow frame and the second lower hollow frame from floating up from therail.
 19. The stacker crane according to claim 14, further comprising: alift platform movable along the first mast and the second mast; a beltattached to the lift platform; and a lifting drive motor configured todrive the belt and mounted in a state tilted with respect to one of theconnecting plates.
 20. The stacker crane according to claim 15, furthercomprising: a lift platform movable along the first mast and the secondmast; a belt attached to the lift platform; and a lifting drive motorconfigured to drive the belt and mounted in a state tilted with respectto one of the connecting plates.
 21. The stacker crane according toclaim 14, further comprising: a controller; and a support member, towhich the controller is attached, fixed to one of the connecting plates.22. The stacker crane according to claim 15, further comprising: acontroller; and a support member, to which the controller is attached,fixed to one of the connecting plates.